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<p>Allows values of floating type to be used directly in expressions.
</p>
<h3><span class="mw-headline" id="Syntax">Syntax</span></h3>
<p>A floating constant is a <a href="value_category.html" title="c/language/value category">non-lvalue</a> expression having the form:
</p>
<table class="t-sdsc-begin">

<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td class="t-sdsc-nopad"> <span class="t-spar">significand</span> <span class="t-spar">exponent</span><span class="t-mark">(optional)</span> <span class="t-spar">suffix</span><span class="t-mark">(optional)</span>
</td>
<td class="t-sdsc-nopad">
</td>
<td class="t-sdsc-nopad">
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr></table>
<p>Where the <span class="t-spar">significand</span> has the form
</p>
<table class="t-sdsc-begin">

<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td class="t-sdsc-nopad"> <span class="t-spar">whole-number</span><span class="t-mark">(optional)</span> <code><b>.</b></code><span class="t-mark">(optional)</span> <span class="t-spar">fraction</span><span class="t-mark">(optional)</span>
</td>
<td class="t-sdsc-nopad">
</td>
<td class="t-sdsc-nopad">
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr></table>
<p>The <span class="t-spar">exponent</span> has the form
</p>
<table class="t-sdsc-begin">

<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <code><b>e</b></code> | <code><b>E</b></code> <span class="t-spar">exponent-sign</span><span class="t-mark">(optional)</span> <span class="t-spar">digit-sequence</span>
</td>
<td> (1)
</td>
<td class="t-sdsc-nopad">
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <code><b>p</b></code> | <code><b>P</b></code> <span class="t-spar">exponent-sign</span><span class="t-mark">(optional)</span> <span class="t-spar">digit-sequence</span>
</td>
<td> (2)
</td>
<td> <span class="t-mark-rev t-since-c99">(since C99)</span>
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr></table>
<div class="t-li1"><span class="t-li">1)</span> The exponent syntax for a decimal floating-point constant</div>
<div class="t-li1"><span class="t-li">2)</span> The exponent syntax for hexadecimal floating-point constant</div>
 <table class="t-rev-begin">
<tr class="t-rev t-since-c23"><td>
<p>Optional single quotes (<code>'</code>) can be inserted between the digits as a separator, they are ignored when compiling.
</p>
</td>
<td><span class="t-mark-rev t-since-c23">(since C23)</span></td></tr>
</table>
<h3><span class="mw-headline" id="Explanation">Explanation</span></h3>
 <table class="t-rev-begin">
<tr class="t-rev t-since-c99"><td>
<p>If the <span class="t-spar">significand</span> begins with the character sequence <code>0x</code> or <code>0X</code>, the floating constant is a <i>hexadecimal floating constant</i>. Otherwise, it is a <i>decimal floating constant</i>.
</p><p>For a <i>hexadecimal floating constant</i>, the <span class="t-spar">significand</span> is interpreted as a hexadecimal rational number, and the <span class="t-spar">digit-sequence</span> of the exponent is interpreted as the integer power of 2 to which the significand has to be scaled.
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw4">double</span> d <span class="sy1">=</span> 0x1.2p3<span class="sy4">;</span> <span class="co1">// hex fraction 1.2 (decimal 1.125) scaled by 2^3, that is 9.0</span></pre></div></div>
</td>
<td><span class="t-mark-rev t-since-c99">(since C99)</span></td></tr>
</table>
<p>For a <i>decimal floating constant</i>, the <span class="t-spar">significand</span> is interpreted as a decimal rational number, and the <span class="t-spar">digit-sequence</span> of the exponent is interpreted as the integer power of 10 to which the significand has to be scaled.
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw4">double</span> d <span class="sy1">=</span> <span class="nu19">1.2e3</span><span class="sy4">;</span> <span class="co1">// decimal fraction 1.2 scaled by 10^3, that is 1200.0</span></pre></div></div>
<h4><span class="mw-headline" id="Suffixes">Suffixes</span></h4>
<p>An unsuffixed floating constant has type <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">double</span></span></span>. If <span class="t-spar">suffix</span> is the letter <code><b>f</b></code> or <code><b>F</b></code>, the floating constant has type <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">float</span></span></span>. If <span class="t-spar">suffix</span> is the letter <code><b>l</b></code> or <code><b>L</b></code>, the floating constant has type <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">long</span> <span class="kw4">double</span></span></span>.
</p>
 <table class="t-rev-begin">
<tr class="t-rev t-since-c23"><td>
<p>If the implementation predefines macro <code>__STDC_IEC_60559_BFP__</code>, the following suffixes and corresponding floating constants are additionally supported:
</p>
<ul><li> if <span class="t-spar">suffix</span> is <code><b>df</b></code> or <code><b>DF</b></code>, the floating constant has type <span class="t-c"><span class="mw-geshi c source-c">_Decimal32</span></span>;
</li><li> if <span class="t-spar">suffix</span> is <code><b>dd</b></code> or <code><b>DD</b></code>, the floating constant has type <span class="t-c"><span class="mw-geshi c source-c">_Decimal64</span></span>;
</li><li> if <span class="t-spar">suffix</span> is <code><b>dl</b></code> or <code><b>DL</b></code>, the floating constant has type <span class="t-c"><span class="mw-geshi c source-c">_Decimal128</span></span>.
</li></ul>
<p>Suffixes for decimal floating-point types are not allowed in hexadecimal floating constants.
</p>
</td>
<td><span class="t-mark-rev t-since-c23">(since C23)</span></td></tr>
</table>
<h4><span class="mw-headline" id="Optional_parts">Optional parts</span></h4>
<p>If the exponent is present and fractional part is not used, the decimal separator may be omitted:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw4">double</span> x <span class="sy1">=</span> <span class="nu19">1e0</span><span class="sy4">;</span> <span class="co1">// floating-point 1.0 (period not used)</span></pre></div></div>
<p>For decimal floating constants, the <span class="t-spar">exponent</span> part is optional. If it is omitted, the period is not optional, and either the <span class="t-spar">whole-number</span> or the <span class="t-spar">fraction</span> must be present.
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw4">double</span> x <span class="sy1">=</span> <span class="nu0">1</span>.<span class="sy4">;</span> <span class="co1">// floating-point 1.0 (fractional part optional)</span>
<span class="kw4">double</span> y <span class="sy1">=</span> <span class="nu18">.1</span><span class="sy4">;</span> <span class="co1">// floating-point 0.1 (whole-number part optional)</span></pre></div></div>
 <table class="t-rev-begin">
<tr class="t-rev t-since-c99"><td>
<p>For hexadecimal floating constants, the exponent is not optional to avoid ambiguity resulting from an <code><b>f</b></code> suffix being mistaken as a hexadecimal digit.
</p>
</td>
<td><span class="t-mark-rev t-since-c99">(since C99)</span></td></tr>
</table>
<h4><span class="mw-headline" id="Representable_values">Representable values</span></h4>
<p>The result of evaluating a floating constant is either the nearest representable value or the larger or smaller representable value immediately adjacent to the nearest representable value, chosen in an implementation-defined manner (in other words, <a href="../numeric/fenv/FE_round.html" title="c/numeric/fenv/FE round">default rounding direction</a> during translation is implementation-defined).
</p><p>All floating constants of the same source form convert to the same internal format with the same value. Floating constants of different source forms, e.g. <span class="t-c"><span class="mw-geshi c source-c"><span class="nu16">1.23</span></span></span> and <span class="t-c"><span class="mw-geshi c source-c"><span class="nu16">1.230</span></span></span>, need not to convert to the same internal format and value.
</p>
 <table class="t-rev-begin">
<tr class="t-rev t-since-c99"><td>
<p>Floating-point constants may convert to more range and precision than is indicated by their type, if indicated by <span class="t-lc"><a href="../types/limits/FLT_EVAL_METHOD.html" title="c/types/limits/FLT EVAL METHOD">FLT_EVAL_METHOD</a></span>. For example, the constant <span class="t-c"><span class="mw-geshi c source-c"><span class="nu17">0.1f</span></span></span> may act as if it were <span class="t-c"><span class="mw-geshi c source-c">0.1L</span></span> in an expression.
</p><p>The result of evaluating a hexadecimal floating constant, if <span class="t-lc"><a href="../types/limits.html" title="c/types/limits">FLT_RADIX</a></span> is 2, is the exact value represented by the floating constant, correctly rounded to the target type.
</p>
</td>
<td><span class="t-mark-rev t-since-c99">(since C99)</span></td></tr>
</table>
 <table class="t-rev-begin">
<tr class="t-rev t-since-c23"><td>
<p>Floating constants of decimal floating-point type that have the same numerical value <span class="mjax" style="display:none">\(\small x\)</span><span class="mjax-fallback texhtml" style="white-space: nowrap;">x</span> but different quantum exponents, e.g. <span class="t-c"><span class="mw-geshi c source-c"><span class="nu0">1230</span>.<span class="me1">dd</span></span></span>, <span class="t-c"><span class="mw-geshi c source-c">1230.0dd</span></span>, and <span class="t-c"><span class="mw-geshi c source-c">1.23e3dd</span></span>, have distinguishable internal representations.
</p><p>The quantum exponent <span class="mjax" style="display:none">\(\small q\)</span><span class="mjax-fallback texhtml" style="white-space: nowrap;">q</span> of a floating constant of a decimal floating-point type is determined in the manner that <span class="mjax" style="display:none">\(\small 10^q\)</span><span class="mjax-fallback texhtml" style="white-space: nowrap;">10<span class="t-su">q<br></span></span> represents 1 at the place of last digit of the <span class="t-spar">significand</span> when possible. If the quantum exponent <span class="mjax" style="display:none">\(\small q\)</span><span class="mjax-fallback texhtml" style="white-space: nowrap;">q</span> and the coefficient <span class="mjax" style="display:none">\(\small c = x\cdot 10^{-q}\)</span><span class="mjax-fallback texhtml" style="white-space: nowrap;">c=x·10<span class="t-su">-q<br></span></span> determined above cannot represented exactly in the type of the floating constant, <span class="mjax" style="display:none">\(\small q\)</span><span class="mjax-fallback texhtml" style="white-space: nowrap;">q</span> is increased as needed within the limit of the type, and <span class="mjax" style="display:none">\(\small c\)</span><span class="mjax-fallback texhtml" style="white-space: nowrap;">c</span> is reduced correspondingly, with needed rounding. The rounding may result in zero or infinity. If (the possibly rounded) <span class="mjax" style="display:none">\(\small c\)</span><span class="mjax-fallback texhtml" style="white-space: nowrap;">c</span> is still out of the permitted range after <span class="mjax" style="display:none">\(\small q\)</span><span class="mjax-fallback texhtml" style="white-space: nowrap;">q</span> reaches the maximum value, the resulted floating constant has value positive infinity.
</p>
</td>
<td><span class="t-mark-rev t-since-c23">(since C23)</span></td></tr>
</table>
<h3><span class="mw-headline" id="Notes">Notes</span></h3>
<p>Default <a href="../numeric/fenv/FE_round.html" title="c/numeric/fenv/FE round">rounding direction</a> and <a href="../types/limits/FLT_EVAL_METHOD.html" title="c/types/limits/FLT EVAL METHOD">precision</a> are in effect when the floating constants are converted into internal representations, and <a href="../numeric/fenv/FE_exceptions.html" title="c/numeric/fenv/FE exceptions">floating-point exceptions</a> are not raised even if <a href="../preprocessor/impl.html" title="c/preprocessor/impl"><tt>
#pragma STDC FENV_ACCESS</tt></a> is in effect (for execution-time conversion of character strings, <span class="t-lc"><a href="../string/byte/strtof.html" title="c/string/byte/strtof">strtod</a></span> can be used). Note that this differs from <a href="constant_expression.html" title="c/language/constant expression">arithmetic constant expressions</a> of floating type.
</p><p>Letters in the floating constants are case-insensitive<span class="t-rev-inl t-since-c23"><span>, except that uppercase and lowercase cannot be both used in suffixes for decimal floating-point types</span> <span><span class="t-mark-rev t-since-c23">(since C23)</span></span></span>: <span class="t-c"><span class="mw-geshi c source-c"><span class="nu12">0x1</span>.<span class="me1">ep</span><span class="sy2">+</span><span class="nu0">3</span></span></span> and <span class="t-c"><span class="mw-geshi c source-c"><span class="nu12">0X1</span>.<span class="me1">EP</span><span class="sy2">+</span><span class="nu0">3</span></span></span> represent the same floating-point value 15.0.
</p><p>The decimal point specified by <span class="t-lc"><a href="../locale/setlocale.html" title="c/locale/setlocale">setlocale</a></span> has no effect on the syntax of floating constants: the decimal point character is always the period.
</p><p>Unlike integers, not every floating value can be represented directly by decimal <span class="t-rev-inl t-since-c99"><span>or even hexadecimal</span> <span><span class="t-mark-rev t-since-c99">(since C99)</span></span></span> constant syntax<span class="t-rev-inl t-since-c99"><span>: macros <a href="../numeric/math/NAN.html" title="c/numeric/math/NAN"><tt>NAN</tt></a> and <a href="../numeric/math/INFINITY.html" title="c/numeric/math/INFINITY"><tt>INFINITY</tt></a> as well as functions such as <span class="t-lc"><a href="../numeric/math/nan.2.html" title="c/numeric/math/nan">nan</a></span> offer ways to generate those special values</span> <span><span class="t-mark-rev t-since-c99">(since C99)</span></span></span>. Note that <span class="t-c"><span class="mw-geshi c source-c"><span class="nu12">0x1</span>.<span class="me1">FFFFFEp128f</span></span></span>, which might appear to be an IEEE float NaN, in fact overflows to an infinity in that format.
</p><p>There are no negative floating constants; an expression such as <span class="t-c"><span class="mw-geshi c source-c"><span class="sy2">-</span><span class="nu16">1.2</span></span></span> is the <a href="operator_arithmetic.html" title="c/language/operator arithmetic">arithmetic operator</a> unary minus applied to the floating constant <span class="t-c"><span class="mw-geshi c source-c"><span class="nu16">1.2</span></span></span>. Note that the special value negative zero may be constructed with <span class="t-lc">-0.0</span>.
</p>
<h3><span class="mw-headline" id="Example">Example</span></h3>
<div class="t-example"><div class="t-example-live-link"><div class="coliru-btn coliru-btn-run-init">Run this code</div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="co2">#include &lt;stdio.h&gt;</span>
 
<span class="kw4">int</span> main<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>
<span class="br0">{</span>
    <a href="../io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"15.0     = %a<span class="es1">\n</span>"</span>, <span class="nu16">15.0</span><span class="br0">)</span><span class="sy4">;</span>
    <a href="../io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"0x1.ep+3 = %f<span class="es1">\n</span>"</span>, <span class="nu12">0x1</span>.<span class="me1">ep</span><span class="sy2">+</span><span class="nu0">3</span><span class="br0">)</span><span class="sy4">;</span>
 
    <span class="co1">// Constants outside the range of type double.</span>
    <a href="../io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"+2.0e+308 --&gt; %g<span class="es1">\n</span>"</span>,  <span class="nu19">2.0e+308</span><span class="br0">)</span><span class="sy4">;</span>
    <a href="../io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"+1.0e-324 --&gt; %g<span class="es1">\n</span>"</span>,  <span class="nu19">1.0e-324</span><span class="br0">)</span><span class="sy4">;</span>
    <a href="../io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"-1.0e-324 --&gt; %g<span class="es1">\n</span>"</span>, <span class="sy2">-</span><span class="nu19">1.0e-324</span><span class="br0">)</span><span class="sy4">;</span>
    <a href="../io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"-2.0e+308 --&gt; %g<span class="es1">\n</span>"</span>, <span class="sy2">-</span><span class="nu19">2.0e+308</span><span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div></div>
<p>Output:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="text source-text"><pre class="de1">15.0     = 0x1.ep+3
0x1.ep+3 = 15.000000
+2.0e+308 --&gt; inf
+1.0e-324 --&gt; 0
-1.0e-324 --&gt; -0
-2.0e+308 --&gt; -inf</pre></div></div> 
</div>
<h3><span class="mw-headline" id="References">References</span></h3>
<div class="t-ref-std-17">
<ul><li> C17 standard (ISO/IEC 9899:2018): 
</li></ul>
<dl><dd><ul><li> 6.4.4.2 Floating constants (p: 47-48)
</li></ul>
</dd></dl>
</div>
<div class="t-ref-std-11">
<ul><li> C11 standard (ISO/IEC 9899:2011): 
</li></ul>
<dl><dd><ul><li> 6.4.4.2 Floating constants (p: 65-66)
</li></ul>
</dd></dl>
</div>
<div class="t-ref-std-c99">
<ul><li> C99 standard (ISO/IEC 9899:1999): 
</li></ul>
<dl><dd><ul><li> 6.4.4.2 Floating constants (p: 57-58)
</li></ul>
</dd></dl>
</div>
<div class="t-ref-std-c89">
<ul><li> C89/C90 standard (ISO/IEC 9899:1990): 
</li></ul>
<dl><dd><ul><li> 3.1.3.1 Floating constants 
</li></ul>
</dd></dl>
</div>
<h3><span class="mw-headline" id="See_also">See also</span></h3>
<table class="t-dsc-begin">

</table>

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